For an engine of a vehicle, for a purpose of e.g. fuel efficiency, a control operation is executed for effecting a warm-up operation when an engine temperature is low or maintaining an engine temperature substantially constant after rise of the engine temperature. As a cooling system for an engine for that purpose, there is known a system configured such that when a cooling water temperature is low, a thermostat valve is closed for causing cooling water to circulate via a bypass passage, not through a radiator and when the cooling temperature becomes higher, the valve is opened for causing the cooling water to circulate through the radiator, thus maintaining cooling water temperature constant.
Patent Document 1 discloses a solenoid valve for use in such engine cooing system, the solenoid valve having a movable portion provided at an outlet of the engine and urged to a closing direction by a spring. This solenoid valve is rendered into a closed state at time of coil excitation and is rendered into an opened state at time of no coil excitation. Further, with this solenoid valve, when the coil is excited, a valve body is drawn to a valve seat to maintain the closed state, thus stopping flow of cooling water in the entire cooling system. Under this state, as heat inside the engine is not discharged to the outside via the cooling water, warm-up is promoted. Thereafter, upon detection of rise of the temperature inside the engine to a predetermined temperature, the coil of the solenoid valve is rendered into a non-excited state, whereby the solenoid valve will be rendered into the opened state as receiving the fluid pressure of cooling water. With this, an amount of cooling water not heated outside the engine will gush into the engine, thus promoting engine cooling.